Data Replication Using SnapMirror16-3
To replicate data for the first time, the filer transfers all data in all snapshots in the
source volume to the mirror. After the filer finishes transferring the data, it brings the
mirror on-line. This version of the mirror is the base line for future incremental
changes.
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To make incremental changes on the mirror, the filer takes regular snapshots on the
source volume according to the schedule specified in the /etc/snapmirror.conf file. By
comparing the current snapshot with the previous snapshot, the filer determines
what changes it needs to make to synchronize the data in the source volume and the
data in the mirror. For example, if a file is deleted from the source volume, SnapMirror
deletes the corresponding file in the mirror the next time it updates the mirror.
For more information about how SnapMirror uses snapshots to transfer data from the
source volume to the mirror, refer to Snapshots Created During Data Replication.
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When SnapMirror transfers data from one volume to another, it generates two vol-
ume copy operations in the same way as the vol copy command. Refer to Volume
Copy Operations in Chapter 18 for the meaning of a volume copy operation.
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After you replicate a volume, the active file system and all snapshots in the source vol-
ume are available on the mirror. As with any volume, you can export the mirror for
NFS mounting or add a share corresponding to this volume for CIFS sharing.
SnapMirror makes all changes to the mirror at the same time. If you have an open file
in the mirror while the filer is updating the mirror, you do not see the changes immedi-
ately. After the mirror update is finished, if you open the file, you see the changes.
This is similar to the situation where another user changes a file in a regular volume
when you are reading the file. You can see the changes the next time you open the
file.
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The following list describes the differences between a mirror and a regular volume:
A mirror has snapmirrored status, which means that it contains read-only data
and network clients cannot write data to the mirror.
The filer does not create automatic snapshots on the mirror based on the snap-
shot schedule.
You cannot use the qtree create command to create qtrees on a mirror. How-
ever, if qtrees exist in the source volume, the filer mirrors the qtrees to the mirror.
You cannot enable quotas on a mirror.